Keyboard units for portable or laptop computers are typically smaller in size than those for standard or desktop personal computers. Due to space constraints, keyboards for portable computers commonly include only 82 or 83 keys, as opposed to the 101 or 102 keys provided on a standard or "full-size" keyboard. Because of the smaller number of keys on the laptop keyboards, some keys are typically "embedded" in the keyboard, and are available only after a designated control key is activated. Most often, the embedded keys correspond to a number pad which is enabled by activating a "Num Lock" key on the keyboard. After the Num Lock key has been activated, the embedded keys on the keyboard are remapped to generate scan codes corresponding to numeric, rather than alpha, keys.
While these types of embedded number pads do provide access to numeric keys in a keypad configuration, many users of laptop computers would prefer the use of a separate numeric keypad which can be used simultaneously with the other alphanumeric and function keys on the keyboard. A full-size non-embedded keypad is particularly desirable for use with accounting and spreadsheet software programs. Integration of a separate keyboard including a full-size number pad with the existing keyboard, however, is not straightforward, as certain key combinations can interfere and cause inaccurate data to be sent to the system processor. For example, in some instances, when the shift key is pressed on the full-size keyboard in connection with another alphanumeric key, the computer Basic Input/Output System (BIOS) receives the make code for the shift key along with the scan code for the pressed key. In other instances, the shifted scan code is generated by the keyboard itself and then sent to the BIOS. Difficulties can arise when the scan code for a particular key is generated by the keyboard itself. In this case, when the shift key on the laptop keyboard is depressed simultaneously with an alphanumeric key on the full-size keyboard whose scan code is generated by the keyboard, the computer BIOS receives a shift scan code and an unshifted alphanumeric scan code. This can result in alternating shifted/unshifted key values, and in some cases, can cause the system to crash. In addition, use of a full-size keyboard with a portable computer increases the size of the system and significantly limits mobility.